Treasury Secretary Steven Mnuchin signaled that the battle for President Donald Trump’s tax returns might ultimately have to be decided in court.

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“There is a difference in interpretation between Congress and us and the Department of Justice that not only impacts the President in this Congress but has a very big impact on every single taxpayer in weaponizing the IRS,” Mnuchin, told a Senate appropriations subcommittee. “This is why there are three branches of government so if there is a difference of opinion, this will go to the third branch of government to be resolved.”

Patrick Semansky/AP

Treasury Secretary Steven Mnuchin testifies before a House Appropriations subcommittee during a hearing on President Trump’s budget request for Fiscal Year 2020, Tuesday, April 9, 2019, on Capitol Hill in Washington.

The back-and-forth comes just days ahead of the looming subpoena deadline from the House Ways and Means Committee to Treasury Secretary and the IRS Commissioner for six years of President Donald Trump’s tax returns by May 17 and came after Mnuchin ignored Democrats’ earlier request. The president’s lawyers and White House are expected to challenge the move and have argued that Democrats’ request does not serve a legislative purpose, an argument the administration made in its rejection of Democrats’ initial request.